1. Field of the Invention
The present invention relates to a dielectric filter, used for instance in a microwave band, a dielectric duplexer, and a communication apparatus using these.
2. Description of the Related Art
For instance, FIG. 11 shows a structure of this type of conventional dielectric filter. In the following diagrams, shaded portions represent portions where the bare outside of the dielectric block (nonconductive portions) can be seen.
This dielectric filter comprises resonator holes 2a and 2b, and external coupling holes 3a and 3b, provided from a first end face 1a of a dielectric block 1 passing to a second end face 1b opposite thereto, inner conductors being provided on the inner faces of these holes, and an external conductor 6 being provided on the outer face of the dielectric block 1. Unformed portions of the external conductor 6 (nonconductive portions) are provided at the opening regions of the resonator holes 2a and 2b in the first end face 1a, and the inner conductors of the resonator holes 2a and 2b are isolated from the external conductor 6 by the first end face 1a, but lead to the external conductor 6 on the second end face 1b. Furthermore, the external conductor 6 is provided at the opening regions of the external coupling holes 3a and 3b in the first end face 1a, and the inner conductors in the external coupling holes 3a and 3b lead to the external conductor 6 at the first end face 1a. Furthermore, input/output electrodes 7a and 7b are isolated from the external conductor 6, and are provided across the second end face 1b and one side face, leading to the inner conductors of the external coupling holes 3a and 3b. In this constitution, the inner conductors of the resonator holes 2a and 2b are combline-coupled, the inner conductors of the external coupling holes 3a and 3b are interdigitally coupled to their respective adjacent resonator holes 2a and 2b, and this electromagnetic field coupling achieves an external coupling.
In this way, when one side face of a dielectric block is deemed the open terminal of inner conductors in the resonator holes, and in addition, an external coupling is obtained using external coupling holes, external conductor formed regions and unformed regions are needed on one side face. This dielectric filter is manufactured by using nonelectrolytic plating to provide an electrode material on all the outer faces of the dielectric block, comprising resonator holes and external coupling holes, and in all the inner faces of the holes; thereafter, the external conductor at the opening region of the resonator holes on the first side face, and the external conductor around the input/output electrode are removed. This removal of the resonator holes opening region of the first side face is performed by removing the external conductors using sandpaper or the like.
Furthermore, when the open face of one resonator hole of adjacent resonator holes is provided at a first end face, the open face of the other resonator hole is provided at a second end face, and the adjacent resonator holes are interdigitally coupled, external conductor formed regions and unformed regions are needed on both end faces.
However, in the above described prior art dielectric filter, since the external conductors at the opening regions of the resonator holes must be partially removed, and open faces forming the open terminals of the inner conductors of the resonator holes must be provided, there is a problem that the formation operation of the open faces of the resonator holes is difficult, increasing manufacturing costs.
Furthermore, there are problems such as difficult in precisely forming the above open faces, causing variation in the filter characteristics.
On the other hand, the external conductors may be formed on the end faces by a screen printing method, but in this case, the number of manufacturing processes such as conductor paste printing, conductor heating, and the like, is increased, and furthermore, there is a problem that positional deviation, wrinkling of the conductor paste, and the like, will adversely affect the positional precision of the external conductors.
To overcome the above described problems, preferred embodiments of the present invention provide a dielectric filter, a dielectric duplexer, and a communication apparatus using these, wherein open faces of resonator holes can be formed by a simple operation and with high dimensional precision, and which are consequently inexpensive and have superior characteristics.
One preferred embodiment of the present invention provides a dielectric filter or a dielectric duplexer, comprising: a dielectric block having a first end face and a second end face and side faces extending therebetween; a plurality of resonator holes and at least one external coupling hole respectively passing through both end faces; inner conductors provided on inner faces of the resonator holes and the external coupling holes; an external conductor provided on the outer faces of the dielectric block; concavities provided in formation regions of the external coupling holes on the first and the second end face and in the short-circuiting regions of the resonator holes; and the external conductor being removed except from the portions of the concavities in the first end face and the second end face, thereby forming open faces of the resonator holes on the first end face and the second end face.
That is, the open faces of the resonator holes on the side faces, which form the opening faces of the resonator holes, protrude further than the other portions.
According to the above described structure and arrangement, by a simple operation of polishing the opening faces of the resonator holes on the first end face and the second end face, it is possible to remove the external conductor on the entire outer faces of the resonator holes on the first end face and the second end face. That is, the external conductor in the concavities in the first end face and the second end face is not removed, whereby the external conductor can be provided easily and with high precision on the formation regions of the external coupling holes on the first end face and the second end face, and on the short-circuiting faces of the resonator holes, making it possible to obtain superior filter characteristics.
Furthermore, in a structure wherein the open faces of all the resonator holes are provided on the first end face, the concavities are provided in the formation regions of the external coupling holes on the first end face, and the external conductor is removed except from the portions of the concavities in the first end face, thereby forming open faces of the resonator holes on the first end face.
According to the above described structure and arrangement, by the simple operation of polishing the opening faces of the resonator holes on the first end face, it is possible to remove the external conductor from all the outer faces of the resonator holes on the first end face, enabling the open faces of the resonator holes to be provided on the first end face with high precision.
Furthermore, the dielectric filter and the dielectric duplexer according to a preferred embodiment of the present invention comprise external coupling adjustment holes, passing through the concavities in the external coupling holes formation region on the first end face and the second end face, and inner conductors are provided on the inner faces thereof. In this case, the opening portions of the external coupling holes in the concavities, and the opening faces of the external coupling adjustment holes, may be provided at different positions along the axial directions of the holes.
In the above described structure and arrangement, the size of the external coupling can be adjusted by changing the shape of the diameter and the arrangement position of the external coupling holes and the external coupling adjustment holes. Furthermore, the external coupling adjustment holes have a function of cutting off couplings between adjacent resonator holes on either side thereof. Moreover, by changing the shape and depth of the concavities, and changing the length (axial length) of the external coupling holes and the external coupling adjustment holes, it is possible to increase the freedom with which the size of the external coupling can be adjusted and set.
Furthermore, an even greater external coupling can be obtained by connecting input/output electrodes to the inner conductors in the external coupling holes on the second end face, the input/output electrodes being isolated from the external conductor, and interdigitally coupling the inner conductors in the external coupling holes to the inner conductors in adjacent resonator holes. Furthermore, if the input/output electrodes are provided crossing to a side face, the side face on which the input/output electrodes are provided can be a surface mount face.
A constitution is acceptable wherein external coupling means comprising external coupling holes is applied to at least one input/output portion of multiple input and output portions, and the external coupling of the other input/output portions is achieved by the capacitance coupling of the input/output electrodes to the external coupling holes. Furthermore, the input/output electrodes may be connected to the inner conductors in the external coupling holes on the first end face, and isolated from the external conductor, and the inner conductors of the external coupling holes and the inner conductors in the resonator holes adjacent thereto can be combline coupled. Furthermore, the inner conductors of the external coupling holes can be isolated from the external conductor on one end face, without providing input/output electrodes, and metallic input/output terminals which connect to the inner conductors of the external coupling holes can then be inserted.
Furthermore, a communication apparatus according to the present invention comprises the dielectric filter and the dielectric duplexer having the features described above, and therefore, it is inexpensive and has superior characteristics.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.